This invention relates to stacker-reclaimers for depositing bulk material on a stockpile and reclaiming material from the pile.
Stacker-reclaimers are known comprising a forward or main boom that forms part of a boom structure on a luffing and slewing mounting. A conveyor extending along the boom conveys material to be stacked to the front end of the boom to deposit it on a stockpile. To reclaim the material from the stockpile a bucket-wheel or other material-gathering device is mounted at the front end of the boom and collects the material to deposit it on the conveyor, which is then running in the reverse direction. To at least partially counterbalance the weight of the boom and its associated equipment, the boom structure has a shorter tail boom which extends in the opposite direction from the mounting and carries a counterbalance weight at its rear extremity. In this way, the overturning moment on the mounting of the boom structure is reduced and the mounting can be constructed in a simpler and more economical manner.
In order to accommodate an elevating conveyor that delivers the material to the inner end of the main boom, when the stacker-reclaimer is working in the stacking mode, the tail boom must be considerably higher than the main boom and as a result there are variations in the effectiveness of the counterbalance weight when the boom structure is luffed. This arises because, whereas the axis of the main boom extends to the mounting at more or less at the same level as the luffing pivot, so that any point on the boom is displaced vertically or nearly vertically during luffing, the higher position of the tail boom results in the counterbalance weight having a significant horizontal component of displacement in the same luffing movement. The moment produced by the weight about the luffing pivot will then change and to cope with the possible variation the mounting of the boom structure must be capable of resisting a substantially greater resultant moment tending to overturn the boom structure. A more robust mounting construction is therefore demanded and that requirement may even limit the maximum capacity of the stacker-reclaimer.